This invention relates generally to adjustable hinge mounts for the backrest of a seat, particularly a motor vehicle seat and more particularly it relates to an adjustable hinge mount of the type which includes a fixed mount part secured to the seat proper and a tiltable mount part secured to the backrest, a wobble gear assembly including an outer gear formed on one mount part and an inner gear formed on the other mount part, the number of teeth of the two gears differing at least about one tooth, a rotary axle having an eccentric portion supporting one of the gears and a concentric portion supporting the other gear to roll the outer gear in mesh with the inner gear whereby the profiles of teeth of the two gears form continuous curves.
In prior art hinge mounts of the aforedescribed type the teeth both of the outer gear and of the inner gear formed on respective hinged mounts are made by pressing or by fine stamping the toothed sections of the mount parts so that the teeth are integrally shaped on the latter. When stamping normal involute or cycloid tooth profiles, the edge life of tools is relatively short because of the fact that there are sharp transitions between the tooth flanks and the root circle or the crown circle, and also due to the relatively small radius of curvature of the cycloid teeth. For this reason, conventional teeth in adjustable hinged mounts have usually a trochoidal profile. While the trochoids in the range of the root flanks of the outer gear and in the range of the ground flanks of the inner gear are formed approximately by a circular section, the curved portions between respective circular sections have the outline resulting from the rolling of the toothed profile of the outer gear in mesh with the inner gear on the pitch or rolling circle. These curved sections however still have relatively strongly bent areas so that the advantage of stamping lightly bent curves can be achieved at conventional hinged mounts only partially.